CN114928075A - Subsynchronous oscillation control method based on instantaneous active power of power grid line - Google Patents
Subsynchronous oscillation control method based on instantaneous active power of power grid line Download PDFInfo
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/24—Arrangements for preventing or reducing oscillations of power in networks
- H02J3/241—The oscillation concerning frequency
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J2300/00—Systems for supplying or distributing electric power characterised by decentralized, dispersed, or local generation
- H02J2300/20—The dispersed energy generation being of renewable origin
- H02J2300/28—The renewable source being wind energy
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- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
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Abstract
The invention provides a subsynchronous oscillation control method based on instantaneous active power of a power grid line, which comprises the following steps: when the power grid operates in a steady state, recording instantaneous active power and current of a monitoring point; enabling the instantaneous active power to pass through a low-pass filter, obtaining the active power difference value of adjacent sampling points from an output signal and obtaining the average value of the active power difference value in a set time period; extracting all frequency components smaller than the power frequency from the monitoring points, if the current amplitude of each component is larger than or equal to a first threshold value, considering that subsynchronous oscillation occurs in the power grid, taking emergency control measures for the power grid, judging and obtaining the initial power flow active power and the power after the subsynchronous oscillation according to the average value of the active power difference, searching a new energy source station according to the difference of the initial power flow active power and the power after the subsynchronous oscillation, and cutting the new energy source station from the power grid. The invention can monitor whether the power grid has subsynchronous oscillation or not and take emergency control measures for the power grid after the subsynchronous oscillation occurs.
Description
Technical Field
The invention relates to the technical field of power systems and automation thereof, in particular to a subsynchronous oscillation control method based on instantaneous active power of a power grid line.
Background
The construction of a novel power system with a new energy station as a main body is one of important ways for achieving the goals of carbon peak reaching and carbon neutralization, however, the access of high-proportion new energy brings new risks and challenges to the safe and stable operation of the power system.
At present, some subsynchronous oscillation events occur in some practical power grids accessed by large-scale wind power at home and abroad, and due to the control of a wind turbine generator or the interaction of the wind turbine generator and the power grid, the subsynchronous oscillation phenomenon which cannot be converged occurs in the power grid, so that power grid equipment is damaged, and the safe and stable operation of a power system is seriously threatened, therefore, whether the subsynchronous oscillation occurs in the power grid or not needs to be judged in time, and the subsynchronous oscillation phenomenon of the power grid needs to be eliminated after the subsynchronous oscillation occurs.
Disclosure of Invention
The invention aims to provide a control method of subsynchronous oscillation based on instantaneous active power of a power grid line, which can monitor whether subsynchronous oscillation occurs in a power grid and take emergency control measures for the power grid after the subsynchronous oscillation occurs so as to eliminate the subsynchronous oscillation phenomenon of the power grid.
In order to achieve the above object, the present invention provides a method for controlling subsynchronous oscillation based on instantaneous active power of a power grid line, comprising:
step S1: setting monitoring points on a power grid;
step S2: when the power grid runs in a steady state, recording instantaneous active power and current of a line where a monitoring point is located at different time points, enabling all the instantaneous active power to sequentially pass through a low-pass filter, wherein an output signal of the low-pass filter is a curve graph of the instantaneous active power changing along with the time points;
step S3: acquiring active power difference values of adjacent sampling points from the output signal, and acquiring an average value of the active power difference values in a set time period;
step S4: if the average value is greater than or equal to a first threshold value, returning to the step S2, and if the average value is less than the first threshold value, taking the average value as the initial power flow active power;
step S5: extracting frequency components smaller than the power frequency of the power grid from the monitoring points, and judging whether the amplitudes of the currents of all the frequency components are smaller than a second threshold value;
step S6: if so, determining that subsynchronous oscillation does not occur in the power grid, returning to the step S2, if not, determining that subsynchronous oscillation occurs in the power grid, taking emergency control measures for the power grid, and if the active power difference is smaller than the first threshold, taking the average value as the power after the subsynchronous oscillation;
step S7: calculating subsynchronous oscillation power according to the subsynchronous oscillation power and the initial power flow active power, finding out a new energy station according to the flow direction of the subsynchronous oscillation power, and calculating the subsynchronous oscillation participation degree of the new energy station;
step S8: cutting off the new energy station with the participation degree larger than or equal to a first participation degree evaluation index from the power grid; and
step S9: and if the current amplitudes of the rest new energy stations are smaller than a second threshold value, ending the emergency control measure, otherwise, continuing to take the emergency control measure on the power grid, and cutting off the new energy stations with participation degrees which are larger than a second participation degree evaluation index and smaller than the first participation degree evaluation index.
Optionally, in the control method, the number of the monitoring points is several, and each monitoring point sequentially executes steps S2 to S9.
Optionally, in the control method, a value of a cut-off frequency of the low-pass filter is smaller than a value of a sub-synchronous oscillation frequency.
Optionally, in the control method, the method for obtaining the active power difference of adjacent sampling points from the output signal includes:
Δp(t k )＝p dc (t k )-p dc (t k-1 )；
wherein, Δ p (t) k ) As active power difference, p dc (t k ) Is at the t k Active power of point sampling point, p dc (t k-1 ) Is at the t th k-1 And (4) point the active power of the sampling point.
Optionally, in the control method, the method for obtaining the average value of the active power difference values in the set time period includes:
wherein the content of the first and second substances,
for the average value of the active power difference over a set period of time, N ═ Δ T × f sample ，f sample For the sampling frequency, Δ T is a set time period, p dc (t k-1 ) Is at the t k-1 Active power of point sampling point, p dc (t k+N ) Is at the t th k+N And (4) point the active power of the sampling point.
Optionally, in the control method, the set time period is 1 s.
Optionally, in the control method, the first threshold, the second threshold, the first engagement assessment index, and the second engagement assessment index are all set values.
Optionally, in the control method, the method for calculating the subsynchronous oscillation power according to the subsynchronous oscillation power and the initial power flow active power includes:
P SSO ＝P′ 0 -P 0 ；
wherein, P SSO Is sub-synchronous oscillating power, P' 0 Power after subsynchronous oscillation, P 0 Is the initial tidal current active power.
Optionally, in the control method, if P SSO If the current is more than 0, the flow direction of the subsynchronous oscillation power is consistent with that of the initial power flow, and the subsynchronous oscillation source is positioned on one side where the initial power flow flows out; if P SSO If the current is less than 0, the flow direction of the subsynchronous oscillation power is opposite to that of the active power of the initial power flow, and the subsynchronous oscillation source is positioned on one side where the active power of the initial power flow flows.
Optionally, in the control method, the method for calculating the participation degree of the subsynchronous oscillation of the new energy station includes:
arranging the subsynchronous oscillation power of the new energy station in a descending order, and numbering the subsynchronous oscillation power in the order;
calculating the participation degree of the subsynchronous oscillation of the new energy station by using the following formula:
wherein, P SSO,i The subscript i (i, 2, 3.) in (a) denotes the subsynchronous oscillation power, σ, of the ith new energy station in descending order i For the participation of the subsynchronous oscillations of the ith new energy station, P SSO,1 The subsynchronous oscillation power of the 1 st new energy station.
Optionally, in the control method, the greater the value of the participation degree is, the greater the possibility that the new energy station is an oscillation source is.
Optionally, in the control method, at least one oscillation source is provided.
In the control method of the subsynchronous oscillation based on the instantaneous active power of the power grid line, provided by the invention, whether the subsynchronous oscillation occurs in the power grid can be monitored, and an emergency control measure is taken for the power grid after the subsynchronous oscillation occurs so as to eliminate the subsynchronous oscillation phenomenon of the power grid. Therefore, the power grid equipment is protected from being damaged, and the power system is enabled to operate safely and stably.
Drawings
Fig. 1 is a flowchart of a control method of subsynchronous oscillation based on instantaneous active of a power grid line according to an embodiment of the present invention.
Detailed Description
The following describes in more detail embodiments of the present invention with reference to the schematic drawings. The advantages and features of the present invention will become more apparent from the following description. It is to be noted that the drawings are in a very simplified form and are not to precise scale, which is merely for the purpose of facilitating and distinctly claiming the embodiments of the present invention.
In the following, the terms "first," "second," and the like are used for distinguishing between similar elements and not necessarily for describing a particular sequential or chronological order. It is to be understood that the terms so used are interchangeable under appropriate circumstances. Similarly, if a method described herein comprises a series of steps, the order in which these steps are presented herein is not necessarily the only order in which these steps can be performed, and some of the described steps may be omitted and/or some other steps not described herein may be added to the method.
The method takes the line active power of the power grid after subsynchronous oscillation as a monitoring object, obtains subsynchronous oscillation power distribution conditions by calculating the variation of the line active power, and reversely traces to the new energy station, thereby judging the participation degree of each station in the oscillation, guiding the emergency control measures after the oscillation according to the participation degree, and ensuring that the oscillation is eliminated after the measures are taken. Namely, the instantaneous active power of the line is monitored in real time; obtaining and recording the active power of the initial power flow of the line and the active power after the subsynchronous oscillation of the line through signal processing; calculating the active power variation, and reversely tracing to the new energy station; and calculating the participation degree of each station and determining a control target of each wheel. The basic principle can be understood as follows: after the subsynchronous oscillation occurs, the active power of each line changes relative to the initial tidal current active power and can be decomposed into a direct current component and an oscillating alternating current component, wherein the direct current component is equal to the algebraic sum of the initial tidal current active power and the subsynchronous oscillation power. The initial tidal current active power of the line is monitored in real time, the variation of the initial tidal current active power before and after oscillation is calculated, and the source of the subsynchronous oscillation power can be judged, so that emergency control after oscillation is guided. Referring to fig. 1, the present invention provides a method for controlling subsynchronous oscillation based on instantaneous active power of a power grid line, including:
step S1: setting monitoring points on a power grid;
step S2: when the power grid operates in a steady state, recording instantaneous active power and current of a line where a monitoring point is located at different time points, enabling all the instantaneous active power to sequentially pass through a low-pass filter, wherein an output signal of the low-pass filter is a curve graph of the instantaneous active power changing along with the time points;
step S3: obtaining the active power difference value of adjacent sampling points from the output signal, and simultaneously obtaining the average value of the active power difference value in a set time period;
step S4: if the average value is greater than or equal to the first threshold value, returning to the step S2, and if the average value is less than the first threshold value, taking the average value as the initial power flow active power;
step S5: extracting frequency components smaller than the power frequency of the power grid from the monitoring points, and judging whether the amplitudes of the currents of all the frequency components are smaller than a second threshold value;
step S6: if so, determining that the subsynchronous oscillation does not occur in the power grid, returning to the step S2, if not, determining that the subsynchronous oscillation occurs in the power grid, taking emergency control measures for the power grid, and if the active power difference is smaller than a first threshold, taking the average value as the power after the subsynchronous oscillation;
step S7: calculating subsynchronous oscillation power according to the power after subsynchronous oscillation and the initial power flow active power, searching the new energy station according to the flow direction of the subsynchronous oscillation power, and calculating the participation degree of the subsynchronous oscillation of the new energy station;
step S8: cutting off the new energy station with the participation degree larger than or equal to the first participation degree evaluation index from the power grid; and
step S9: if the current amplitudes of the rest new energy stations are smaller than the second threshold value, ending the emergency control measure, otherwise, continuing to take the emergency control measure for the power grid, cutting off the new energy stations with the participation degree larger than the second participation degree evaluation index and smaller than the first participation degree evaluation index, and ending the emergency control measure no matter what the states of the rest new energy stations are cut off.
The instantaneous active power can be obtained by directly adopting a synchronous vector measurement unit (PMU) device configured in the current power grid to calculate monitoring signals of three-phase voltage and current, and the expression of the instantaneous active power is as follows:
P i-j,0 (t)＝u a (t)*i a (t)+u b (t)*i b (t)+u c (t)*i c (t)；
wherein, P i-j,0 (t) is the instantaneous active power at time t, u a (t)、u b (t) and u c (t) is divided intoInstantaneous value of three-phase voltage, i, identifying the monitoring point at time t a (t)、i b (t) and i c And (t) represents the instantaneous value of the three-phase current flowing out of the monitoring point at the time t. Theoretically, instantaneous active power is monitored all the time, and similarly, whether subsynchronous oscillation occurs in the power grid is also judged all the time, so that the time t is changed all the time, and the monitored instantaneous active power is real-time data and is changed along with the time. Once a certain data is judged to have subsynchronous oscillation, an emergency control measure needs to be taken to solve the subsynchronous oscillation, and if the subsynchronous oscillation does not occur at the moment, whether the subsynchronous oscillation occurs to the power grid at the next moment or not is continued.
Preferably, the number of the monitoring points is several, and each monitoring point sequentially executes the steps S2 to S9. The new energy station generates electric power and transmits the electric power to various places through a power grid, multiple transmission lines are available, whether subsynchronous oscillation occurs or not can be judged through the current or instantaneous active power value on the lines, meanwhile, the new energy station is traced back according to the lines on which the subsynchronous oscillation occurs, and emergency control measures are taken for the new energy station. Therefore, a plurality of monitoring points can be set according to the setting of the circuit, the data of each monitoring point is separately monitored and separately judged, whether subsynchronous oscillation occurs or not is judged by monitoring the current and instantaneous active power values of the monitoring points, once the current and instantaneous active power values of a certain monitoring point can be judged to be subsynchronous oscillation, a corresponding new energy station needs to be found according to the monitoring point, and an emergency control measure is taken for the new energy station.
Preferably, the value of the cut-off frequency of the low-pass filter (LPF) is smaller than the value of the subsynchronous oscillation frequency. The cutoff frequency of the low-pass filter is set with reference to the frequency at which subsynchronous oscillation has occurred in history, and for example, the value of the cutoff frequency of the low-pass filter of the embodiment of the present invention may be taken as f c 1 Hz. Only the instantaneous active power of low frequency is outputted after passing through the low pass filter, and since the instantaneous active power of the monitoring point is constantly monitored and the instantaneous active power is constantly inputted to the low pass filter in step S2, the instantaneous active power is lowThe value of the output of the pass filter also changes, so the value of the sampling point also changes, so the active power difference value and the average value of the active power difference value also change. Therefore, the active power difference value and the average value of the active power difference value may be changed after returning to step S2.
Preferably, the method for obtaining the active power difference of adjacent sampling points from the output signal includes:
Δp(t k )＝p dc (t k )-p dc (t k-1 )；
wherein, Δ p (t) k ) As difference in active power, p dc (t k ) Is at the t th k Active power of point sampling point, p dc (t k-1 ) Is at the t k-1 Active power at the point sampling point, t k Point sum t k-1 The points are adjacent sampling points, which may change as time t changes.
Preferably, the method for obtaining the average value of the active power difference values in the set time period includes:
wherein the content of the first and second substances,
for the average value of the active power difference over a set period of time, N ═ Δ T × f sample ，f sample For the sampling frequency, Δ T is a set time period, p dc (t k-1 ) Is at the t k-1 Active power of point sampling point, p dc (t k+N ) Is at the t k+N And (4) point the active power of the sampling point. The set time period deltat of the embodiment of the invention is chosen to be 1s,
to calculate Δ p (t) k ) The average value over a time window (T, T + Δ T), the time of T varying,
may also vary in value.
Preferably, the first threshold value, the second threshold value, the first engagement assessment indicator and the second engagement assessment indicator are all set values. First threshold value epsilon 1 The method is used for avoiding the error recording of the active power change of the line caused by the tidal current mode as a steady-state tidal current value, and the first threshold value epsilon 1 The method is determined according to the variation range of the line power measurement value in the actual operation of the current power grid, and can generally take the value of epsilon 1 1 MW. Second threshold value I thre Can be set according to the actual condition of the power grid, is used for judging whether subsynchronous components exist in the current and can be taken as I thre ＝5％I dc In this embodiment, set I thre 0.1 kA. In step S5, the frequency component is extracted, the current at the monitoring point may be subjected to fast fourier analysis, and then the current amplitudes I of all frequency points below the power frequency are extracted ω,i If all of I ω,i Are all less than a threshold value I thre Deeming the grid to not have subsynchronous oscillations, wherein the current amplitude I ω,i Indicating the magnitude of the current for the ith frequency component. First participation evaluation indicator eta 1 And a second participation evaluation index eta 2 The relative relationship between the oscillation sources is determined in the emergency control of the separate wheel according to the actually set index of the current power grid, for example, η is set in the embodiment 1 ＝95％、η 2 ＝90％。
Preferably, the method for calculating the subsynchronous oscillation power includes:
P SSO ＝P′ 0 -P 0 ；
wherein, P SSO Is sub-synchronous oscillatory power, P' 0 Power after subsynchronous oscillation, P 0 Is the initial tidal current active power. The average value of real time satisfying different conditions can be calculated according to the steps S4 to S6
And the power is used for calculating the subsynchronous oscillation power as the initial power flow active power or the power after subsynchronous oscillation. With time, the average value isThe current is constantly changing, so that the situation that the current is larger than the first threshold and smaller than the first threshold, subsynchronous oscillation occurs and subsynchronous oscillation does not occur may occur, and when any situation occurs, the current corresponding to the current at the current time point is searched back.
In step S2, the direction of the instantaneous active power may be defined, for example, by defining P i-j,0 The direction of (t) > 0 is a positive direction, so the positive and negative direction judgment of the power after subsynchronous oscillation and the initial power flow active power is consistent with the direction judgment of the instantaneous active power, namely, the positive direction of the power after subsynchronous oscillation and the initial power flow active power is the positive direction of the instantaneous active power. If P SSO If the current is more than 0, the flow direction of the subsynchronous oscillation power is consistent with that of the initial power flow, and the subsynchronous oscillation source is positioned on one side where the initial power flow flows out; if P SSO If the current is less than 0, the flow direction of the subsynchronous oscillation power is opposite to that of the active power of the initial power flow, and the subsynchronous oscillation source is positioned on one side where the active power of the initial power flow flows.
Preferably, the method for calculating the participation degree of the subsynchronous oscillation of the new energy station comprises the following steps:
arranging the subsynchronous oscillation power of the new energy station in a descending order, and numbering the subsynchronous oscillation power in the order;
calculating the participation degree of the subsynchronous oscillation of the new energy station by using the following formula:
wherein, P SSO,i The subscript i (i, 2, 3.) in (a) denotes the subsynchronous oscillation power, σ, of the ith new energy station in descending order i For the degree of participation of the subsynchronous oscillations of the ith new energy station, P SSO,1 The subsynchronous oscillation power of the 1 st new energy station. Specifically, the subsynchronous oscillation power P obtained in step S7 SSO The power flow direction of the new energy field station can be traced back to the node of the new energy field station to obtain the oscillation power P of each new energy field station in the subsynchronous oscillation SSO,i Size and breadth(Table i below shows the stations of different new energy stations) and directions, and according to P SSO,i Sequencing from big to small, and simultaneously calculating the subsynchronous oscillation participation degree sigma of each new energy station i Obtaining P SSO And (6) sorting.
Preferably, the degree of engagement σ i The greater the value of (a), the greater the likelihood that the new energy station is an oscillating source. At least one oscillation source is provided, and obviously, the participation degree is calculated after the subsynchronous oscillation is judged to occur, so that the traced new energy station has one oscillation source according to P SSO,i Arranged from large to small, so P SSO,1 Is an oscillation source. Further, the engagement σ i The larger the value of (a) is, the ith new energy station and P are represented SSO,1 The greater the likelihood of being an oscillating source at the same time. Multiple sources of oscillation may exist during subsynchronous oscillation, by σ i Multiple sources can be judged at one time, and the emergency control can be guided conveniently.
Specifically, in the embodiment of the present invention, 6 monitoring points are used as an example, a new energy centralized access area in a certain power grid is used as an implementation object, 6 new energy stations in the area respectively transmit power to a main grid through 6 lines, the monitoring points are respectively set on the 6 lines, and instantaneous active power of the line where the 6 monitoring points are located is shown in table 1.
TABLE 1
If the power grid has subsynchronous oscillation, an
Recording the current average value as the subsynchronous oscillation post-power P' 0 And calculating the power variation as the subsynchronous oscillation power P SSO 。
Wherein the subsynchronous oscillation power P SSO The expression is as follows:
P SSO ＝P′ 0 -P 0 。
if P SSO > 0, denotes nextThe synchronous oscillation power flow direction is consistent with the initial power flow, the oscillation source is positioned at the active outflow side of the initial power flow, and if P is equal to the initial power flow SSO If < 0, it means that the subsynchronous oscillation power flows in the opposite direction to the initial power flow, the oscillation source is positioned at the side where the initial power flow successfully flows in, P SSO The larger the power is, the larger the subsynchronous oscillation power provided by the power outflow side is, the closer to the oscillation source is. Then according to P SSO Judging the power flow direction of the line, and reversely tracing to the new energy station node to obtain the oscillation power P of each new energy station in the subsynchronous oscillation SSO,i Size and direction, and according to P SSO,i Sequencing from big to small, and simultaneously calculating subsynchronous oscillation participation degree sigma of each new energy station i . Subsynchronous oscillation participation σ i The expression of (c) is:
after the above steps are completed, the subsynchronous vibration power distribution and the participation degree can be obtained as shown in table 2:
TABLE 2
| Monitoring point | ① | ② | ③ | ④ | ⑤ | ⑥ |
| P SSO /MW | 7.35 | 1.27 | -7.1 | 0.06 | -0.07 | 0.49 |
| σ i | 100％ | 17.3％ | —— | 0.8％ | —— | 6.7％ |
Therefore, the new energy stations are sequenced from large to small, namely, the stations are sequenced to be a monitoring point, a monitoring point and a monitoring point, and the other two monitoring points are not positioned on the side of the oscillation source.
Then, take emergency control measures, the first round will σ i ≥η 1 All stations are cut off and whether subsynchronous oscillation disappears or not is judged. If the oscillation disappears, ending the emergency control measure, if the oscillation does not end, continuing the second round of control, and remaining eta in the station 1 ＜σ i ＜η 2 And (4) cutting off all the stations, and finishing the emergency control measures after the two-wheel control, no matter whether the oscillation disappears. Therefore, in this embodiment, the station (i) is determined to be the only oscillation source in combination with the engagement indicator. The subsynchronous oscillation of the wind turbine generator of the station I is eliminated, so that the emergency control can be finished by only one turn of the wind turbine generator, and the oscillation suppression is finished.
In summary, in the control method for sub-synchronous oscillation based on instantaneous active power of the power grid line provided by the embodiment of the present invention, whether the power grid generates sub-synchronous oscillation or not can be monitored, and an emergency control measure is taken for the power grid after the sub-synchronous oscillation occurs, so as to eliminate the sub-synchronous oscillation phenomenon of the power grid. Therefore, the power grid equipment is protected from being damaged, and meanwhile, the power system is enabled to operate safely and stably.
The above description is only a preferred embodiment of the present invention, and does not limit the present invention in any way. Any person skilled in the art can make any equivalent substitutions or modifications on the technical solutions and technical contents disclosed in the present invention without departing from the scope of the technical solutions of the present invention, and still fall within the protection scope of the present invention without departing from the technical solutions of the present invention.
Claims (12)
1. A control method of subsynchronous oscillation based on instantaneous active power of a power grid line is characterized by comprising the following steps:
step S1: setting monitoring points on a power grid;
step S2: when the power grid operates in a steady state, recording instantaneous active power and current of a line where a monitoring point is located at different time points, enabling all the instantaneous active power to sequentially pass through a low-pass filter, wherein an output signal of the low-pass filter is a curve graph of the instantaneous active power changing along with the time points;
step S3: acquiring active power difference values of adjacent sampling points from the output signal, and acquiring an average value of the active power difference values in a set time period;
step S4: if the average value is greater than or equal to the first threshold value, returning to the step S2, and if the average value is less than the first threshold value, taking the average value as the initial power flow active power;
step S5: extracting frequency components smaller than the power frequency of the power grid from the monitoring points, and judging whether the amplitudes of the currents of all the frequency components are smaller than a second threshold value;
step S6: if so, determining that subsynchronous oscillation does not occur in the power grid, returning to the step S2, if not, determining that subsynchronous oscillation occurs in the power grid, taking emergency control measures for the power grid, and if the active power difference is smaller than the first threshold, taking the average value as the power after the subsynchronous oscillation;
step S7: calculating subsynchronous oscillation power according to the power after the subsynchronous oscillation and the initial power flow active power, finding out a new energy station according to the flow direction of the subsynchronous oscillation power, and calculating the participation degree of the subsynchronous oscillation of the new energy station;
step S8: cutting off the new energy station with the participation degree larger than or equal to a first participation degree evaluation index from the power grid; and
step S9: if the current amplitudes of the rest new energy stations are smaller than the second threshold value, ending the emergency control measure, otherwise, continuing to take the emergency control measure on the power grid, and cutting off the new energy stations with participation degrees larger than a second participation degree evaluation index and smaller than the first participation degree evaluation index.
2. The control method according to claim 1, wherein the number of the monitoring points is several, and each of the monitoring points sequentially performs steps S2 to S9.
3. A control method according to claim 1, characterized in that the value of the cut-off frequency of the low-pass filter is smaller than the value of the subsynchronous oscillation frequency.
4. The control method of claim 1, wherein the step of obtaining the active power difference between adjacent samples from the output signal comprises:
Δp(t k )＝p dc (t k )-p dc (t k-1 )；
wherein, Δ p (t) k ) As difference in active power, p dc (t k ) Is at the t k Active power of point sampling point, p dc (t k-1 ) Is at the t th k-1 And (4) point the active power of the sampling point.
5. The control method according to claim 1, wherein the method of obtaining the average value of the active power difference value in the set time period comprises:
wherein the content of the first and second substances,
for the average value of the active power difference over a set period of time, N ═ Δ T × f sample ，f sample For the sampling frequency, Δ T is a set time period, p dc (t k-1 ) Is at the t k-1 Active power of point sampling point, p dc (t k+N ) Is at the t th k+N And (4) point the active power of the sampling point.
6. The control method according to claim 1 or claim 4, characterized in that the set period of time is 1 s.
7. The control method according to claim 1, characterized in that the first threshold value, the second threshold value, the first engagement assessment indicator and the second engagement assessment indicator are all set values.
8. The control method according to claim 1, wherein the method for calculating the subsynchronous oscillation power according to the subsynchronous oscillation power and the initial power flow active power comprises:
P SSO ＝P′ 0 -P 0 ；
wherein, P SSO Is sub-synchronous oscillatory power, P' 0 Power after subsynchronous oscillation, P 0 Is the initial power flow active power.
9. The control method of claim 8, wherein if P is SSO If the current is more than 0, the flow direction of the subsynchronous oscillation power is consistent with that of the initial power flow active power, and the subsynchronous oscillation source is positioned on one side where the initial power flow active power flows out; if P SSO If < 0, the subsynchronous oscillationThe flow direction of the oscillation power is opposite to that of the active power of the initial power flow, and the subsynchronous oscillation source is positioned on one side into which the active power of the initial power flow flows.
10. The control method according to claim 1, wherein the method of calculating the engagement of the subsynchronous oscillations of the new energy site comprises:
arranging the subsynchronous oscillation power of the new energy station in a descending order, and numbering the subsynchronous oscillation power in the order;
calculating the participation degree of the subsynchronous oscillation of the new energy station by using the following formula:
wherein, P SSO,i The subscript i (i, 2, 3.) in (a) denotes the subsynchronous oscillation power, σ, of the ith new energy station in descending order i For the participation of the subsynchronous oscillations of the ith new energy station, P SSO,1 The subsynchronous oscillation power of the 1 st new energy station.
11. The control method of claim 10, wherein the greater the value of the engagement, the greater the likelihood that the new energy station is an oscillating source.
12. The control method of claim 11, wherein there is at least one of said oscillation sources.
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